The present invention is directed to a device of the type generally known as a crank connector to be positioned between the lower part of a drill string and a down hole motor rotating a drill bit, the crank connector being of the type which allows adjustment of the orientation of the drill path.
There have been various methods and devices proposed previously for carrying out directional drilling. According to one device described in U.S. Pat. No. 3,365,007, the action of an appropriately directed fluid jet is used for locally destroying ground formations so as to create a recess into which the drill bit will be diverted. An obvious disadvantage of such a device is its lack of accuracy because the jet action of the fluid jet and thus, the resulting bit deflection, will vary substantially depending on the hardness of the geological formations through which drilling is being performed. Another disadvantage is that is becomes necessary to use a specially designed drill bit provided with a nozzle for discharging the fluid jet.
According to another well known method, described for example in British Pat. No. 1,139,908, U.S. Pat. Nos. 3,593,810, 3,888,319, and 4,040,494, and in French Pat. No. 2,297,989, there is used a deflecting device which surrounds a section of the drill string at its lower part, normally in the vicinity of the drill bit. The deflecting device includes a plurality of radially extending fingers which are displaceable with respect to the drill string axis. These fingers are suitably displaced so as to bear on the wall of the drilled bore hole, thereby making it possible to offset the drill bit axis with respect to the bore hole axis and thereby resulting in a deflection of the drilling direction. The use of such devices requires that drilling be discontinuous since the drilling is performed in successive runs between which drilling is stopped to permit the displacement of the deflecting device, and started again in the new direction. This results in a considerable amount of time lost which increases the cost of each drilling operation.
In drilling devices which make use of a down hole motor, it has been proposed to locate the crank connector of selected angle between the lower part of the drill string and the so called drill head (i.e., the assembly of the drill bit and of the down hole motor). However, every time the drilling direction is to be changed, it becomes necessary that the whole drill string be raised to the ground surface to change the crank connector to another one of appropriate angle, the angle being selected in accordance with the desired deflection.
New so-called hinged crank connectors have been described in French Pat. No. 1,252,703, and mentioned in French Pat. No. 2,175,620. These type of connectors usually comprise two tubular parts hinged to each other which can only take two relative positions. In a first position, the two parts of the connector are aligned (the angle of the connector is equal to zero), while in the second position, the two parts are located at a preselected angle with respect to each other. As with the previously described crank connectors, it becomes necessary that at least one element of the connector be raised to the surface when the desired drilling deflection is not compatible with the angle that the two parts of the connector can form with respect to each other.